The apparatus disclosed herein, in general, relates to electrical enclosures. More particularly, the apparatus disclosed herein relates to electrical enclosures that provide, for example, front access only, and front and rear access herein referred to a “multi-access”, to electrical bus members, multiple electrical components, and apparatuses housed within the electrical enclosures. Furthermore, the apparatus disclosed herein relates to electrical bus assemblies for electrical enclosures and arc resistant electrical enclosures.
Medium voltage electrical components and apparatuses, for example, circuit breakers, potential transformers, current transformers, control power transformers, etc., are often housed in an electrical enclosure called a switchgear cabinet. The medium voltage electrical components and apparatuses operate, for example, in a range of about 1000 volts to about 100,000 volts. The switchgear cabinet for medium voltage equipment typically occupies a large space and is difficult to access. As such, maintenance and space considerations are driving factors in the design of new electrical equipment. There is a need for constructing a switchgear assembly that makes efficient use of the available floor space and minimizes the time required for inspection, repair and maintenance of equipment accommodated within the switchgear assembly.
Switchgear cabinets, particularly medium voltage metal clad switchgear cabinets are often damaged due to arcing. An explosion caused by arcing within a switchgear cabinet results in significant economic loss due to interruption of energy distribution, and damage of the switchgear cabinet and the electrical components or equipment accommodated in the switchgear cabinet. Consequently, maintenance personnel inspecting and servicing the switchgear cabinets have to wear protective gear that is bulky and expensive. Typical arc resistant switchgear cabinets tend to be very large and often have heavy sheet metal enclosures. Such configurations require significant space. Some switchgear cabinets employ an external arcing chamber that limits the configuration of the electrical components, equipment, etc., within the switchgear cabinet.
Conventional switchgear cabinets typically provide only a single access, that is, a front access or a rear access to the electrical components and electrical cables within the switchgear cabinet, which places restrictions on the arrangement of the electrical components and the electrical cables within the switchgear cabinet. Therefore, single access switchgear cabinets do not make an efficient use of the available floor space owing to the lesser flexibility available in positioning the electrical components and the electrical cables within the switchgear cabinet. Moreover, conventional single access switchgear cabinets do not allow accommodation of multiple electrical components along with electrical cables in a single section. Hence, there is a need for a switchgear cabinet that provides both front access and rear access to the electrical components and the electrical cables for providing increased flexibility in positioning of the electrical components and the electrical cables within the switchgear cabinet, which results in efficient use of space and flexible accessibility. Moreover, there is a need for a switchgear cabinet that enables accommodation of multiple electrical components in a single section of the switchgear cabinet, thereby minimizing requirement of additional sections.
Furthermore, conventional switchgear cabinets utilize bar type current transformers that are mounted in the rear making it difficult to replace a transformer in the field if one of the transformers fail. Therefore, there is a need for mounting transformers and other electrical components in the front of the switchgear cabinet for easier accessibility for maintenance and inspection.
Moreover, there are significant limitations with respect to the size of potential transformers and control power transformers that are available in conventional switchgear cabinets. For example, the maximum voltage for a potential transformer in a conventional metal clad switchgear cabinet is about 5000V and the maximum power for a control power transformer is about 5 kVA.
Conventional metal clad switchgear cabinets for the North American market need to meet stringent Institute of Electrical and Electronics Engineers (IEEE) requirements and American National Standards Institute (ANSI) requirements. These standards require a circuit breaker to be tested inside the switchgear cabinets that have limited cooling and therefore limiting the temperature rise within the switchgear cabinet becomes a major challenge. Furthermore, as per International Electrotechnical Commission (IEC) standards, barriers between compartments in the switchgear cabinets are not a requirement, therefore cooling the circuit breaker within the switchgear cabinet is much easier. IEC designed equipment, would have to be derated significantly if no changes are made.
Furthermore, conventional metal clad switchgear cabinets pose additional challenges to meet ANSI and Underwriters Laboratories (UL) requirements because of limited space and limited cooling. In addition, IEEE/ANSI designed equipment requires bus bars within the switchgear cabinet to be insulated, making it more difficult to cool the critical current carrying bus bars in certain compartments of the switchgear cabinet that accommodate the circuit breaker. Alternatively, expensive heat sinks have to be employed to limit temperature rise. The addition of heat sinks is a difficult task in the compact space available and poses significant challenges to pass the required lightning impulse test due to space limitations and the shape of the heat sink.
Hence, there is a long felt but unresolved need for an arc resistant metal clad switchgear assembly that has a compact footprint and provides either front access only, or front access and rear access herein referred to as “multi-access” to electrical components, electrical cables, and equipment accommodated in the switchgear assembly for inspection, testing and maintenance with limited space requirements and without protective gear. Moreover, there is a need for a compact switchgear assembly that allows increased flexibility in positioning of the electrical components and the electrical cables within the switchgear assembly without limitations in configurations of the electrical components, and that also enables accommodation of multiple electrical components along with the electrical cables in a single section of the switchgear assembly. Furthermore, there is a need for a compact switchgear assembly that allows successful testing of the electrical components, for example, circuit breakers that are accommodated in the switchgear assembly without additional heat sinks.